Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 40944 times)

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Offline ValentineWeather

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Yeah wasn't suggesting that was the cure just you may be able to lower dp a little getting away from wet ground. I'm not moving sensors for sure but have tested high up before with unsatisfactory results with both abnormal warm lows and highs lower than normal. 5'-6' is correct elevation.
Randy

Offline Bobvelle

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I want to preface this by saying, I have only read the first half of this thread (~14 pages or so). So if my account is no longer germane, then sorry.  :-P

I have a Davis VP2. Iv'e been getting errors on Dew point from MADIS since I switched to a fan aspirated SHT31 sensor. This particular sensor is only a week old. This and my last SHT31 sensor has shown RH of +8 and Dewpoint of +3-4 degrees according to MADIS and it concerned me.
I live in Louisiana and RH is HIGH as most know. Also, Local airports are showing the same or higher dew points & RH than me almost daily. I've read many people here have little regard for the MADIS ratings and I'll address that too.
I found this thread and decided ..enough is enough!

So today I grabbed 2 Bacharach sling psychs from work. One is a Mercury and about 10 years old (maybe used twice) the other is red spirit and is brand new. Both wet & dry bulb match exactly when dry on both psychrometers.

At test, console shows 37%RH and 65 deg dew point. Temp 95 degrees. It's rather dry here today (Rare) due to a deep trough in the Gulf. Winds have been out of the NNE since yesterday (again, Very rare for July) so measuring mid-range humidity was just lucky timing.

First sling (Mercury) Psych showed 95 Dry and 76 wet worked out to 68 Deg DP , 41.5% RH.
Second (Spirit) showed 93 Dry and 74 Wet worked out to 65 Deg DP 40% RH.

This was done several times as the Temp dropped, and the readings were consistent.

Somebody Is Lying to me  :evil: And there initials are M.A.D.I.S.

If anything, I'm reading a bit dry. So, so far, I trust my station's data. I live in a heavily forested rural area with a Lake 2 miles west of me. I'm satisfied that my reading are correct. Oh and MADIS ?...I'm not re-calibrating anything so you can shove it.  \:D/

The vast amount of information here on this humidity bias and temp/humidity sensors in general is stunning. Most here have forgotten more than I'll ever learn about all this. Iv'e learned a lot and hope to learn more. Keep up the great discussions everyone.
« Last Edit: July 25, 2018, 09:34:28 PM by Bobvelle »

Offline CW2274

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Somebody Is Lying to me  :evil: And there initials are M.A.D.I.S.
Oh and MADIS ?...I'm not re-calibrating anything so you can shove it.  \:D/
All CQ's are done by comparing yourself to neighboring stations, be they good or be they bad. All you can do is what you've done, use common sense and understand your data.
No one knows your PWS better than you.

Offline Bobvelle

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Somebody Is Lying to me  :evil: And there initials are M.A.D.I.S.
Oh and MADIS ?...I'm not re-calibrating anything so you can shove it.  \:D/
All CQ's are done by comparing yourself to neighboring stations, be they good or be they bad. All you can do is what you've done, use common sense and understand your data.
No one knows your PWS better than you.

You're right, and I know that, and I was fine knowing my sensors were correct and they were just 'grading on a curve'...but I guess what got lost in my post (my fault) was that this thread was exacerbating my doubts that 'maybe my sensors are wrong'.  Sorry MADIS, didn't mean to be so rough on ya'

Offline ValentineWeather

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I want to preface this by saying, I have only read the first half of this thread (~14 pages or so). So if my account is no longer germane, then sorry.  :-P

I have a Davis VP2. Iv'e been getting errors on Dew point from MADIS since I switched to a fan aspirated SHT31 sensor. This particular sensor is only a week old. This and my last SHT31 sensor has shown RH of +8 and Dewpoint of +3-4 degrees according to MADIS and it concerned me.
I live in Louisiana and RH is HIGH as most know. Also, Local airports are showing the same or higher dew points & RH than me almost daily. I've read many people here have little regard for the MADIS ratings and I'll address that too.
I found this thread and decided ..enough is enough!

So today I grabbed 2 Bacharach sling psychs from work. One is a Mercury and about 10 years old (maybe used twice) the other is red spirit and is brand new. Both wet & dry bulb match exactly when dry on both psychrometers.

At test, console shows 39%RH and 66 deg dew point. Temp 95 degrees. It's rather dry here today (Rare) due to a deep trough in the Gulf. Winds have been out of the NNE since yesterday (again, Very rare for July) so measuring mid-range humidity was just lucky timing.

First sling (Mercury) Psych showed 95 Dry and 76 wet worked out to 68 Deg DP , 41.5% RH.
Second (Spirit) showed 93 Dry and 74 Wet worked out to 65 Deg DP 40% RH.

This was done several times as the Temp dropped, and the readings were consistent.

Somebody Is Lying to me  :evil: And there initials are M.A.D.I.S.

If anything, I'm reading a bit dry. So, so far, I trust my station's data. I live in a heavily forested rural area with a Lake 2 miles west of me. I'm satisfied that my reading are correct. Oh and MADIS ?...I'm not re-calibrating anything so you can shove it.  \:D/

The vast amount of information here on this humidity bias and temp/humidity sensors in general is stunning. Most here have forgotten more than I'll ever learn about all this. Iv'e learned a lot and hope to learn more. Keep up the great discussions everyone.

All I can say this is abnormal. I would like to look into it further what CWOP station and airport do you compare to?
Randy

Offline CW2274

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Somebody Is Lying to me  :evil: And there initials are M.A.D.I.S.
Oh and MADIS ?...I'm not re-calibrating anything so you can shove it.  \:D/
All CQ's are done by comparing yourself to neighboring stations, be they good or be they bad. All you can do is what you've done, use common sense and understand your data.
No one knows your PWS better than you.
I guess what got lost in my post (my fault) was that this thread was exacerbating my doubts that 'maybe my sensors are wrong'
Ha! Get in an unfortunate line....
This will eventually get figured out, hopefully sooner than later.  :roll:

Offline Bobvelle

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All I can say this is abnormal. I would like to look into it further what CWOP station and airport do you compare to?

I agree. But all I can go by is the list of nearby stations at the bottom of the Data quality page.

EW6758   14.7 miles   North Georgetown, LA, US    -0.6mb   -1.6F   -1.1F
KAEX        17.6 miles South ALEXANDRIA INTERNATIONAL AIRPORT, LA, United States    -0.1mb   -0.6F   1.7F
EW6201   22.7 miles   South       Alexandria, LA, US    0.5mb   -1.1F   0.7F
UP886   22.7 miles   Northeast       Urania, LA,    -0.2F   
KESF          22.9 miles   Southeast       ALEXANDRIA ESLER RGNL AIRPORT , LA,  -0.5mb   0.0F   0.5F
UR391   29.1 miles   South  Wilgln, LA, United States Of America                                     2.2F   
KIER          31.1 miles   West       Natchitoches, Natchitoches Regional Airport, LA,  -0.5mb   -1.8F   1.7F
UP368   34.3 miles   South       Meeker, LA, United States Of America                        -0.3F   
KAQV   42.2 miles   West       Ft. Polk, Peason Ridge, LA, United States                          -0.4mb   -0.7F   2.7F
KBKB   43.1 miles   Southwest       Ft. Polk, Fullerton Landing Strip, LA, United States    -0.1mb   -1.5F   0.6F


And of these that I looked at recently, many of their Quality checks are also flagged for high humidity/dew point.

Oh FYI I'm DW5212 (D5212 MADIS)
« Last Edit: July 25, 2018, 08:22:10 PM by Bobvelle »

Offline ValentineWeather

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Thanks for the location...Really not interested in MADAS but looking at your nearby airport Dewpoint is running about 4 higher. Which is the norm with these sensors.

Can't say anything about the sling readings you got, but they are notorious for giving different readings for different individuals. #1 reason for erratic results was finding appropriate shade. Back in the day ERT training we broke several units with 25 firefighters slinging up next to pumper truck where the only shade was.  :lol: 


https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KAEX
https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=D5212&unit=0&timetype=LOCAL

« Last Edit: July 25, 2018, 08:47:22 PM by ValentineWeather »
Randy

Offline Bobvelle

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Thanks for the location...Really not interested in MADAS but looking at your nearby airport Dewpoint is running about 4 higher. Which is the norm with these sensors.

Can't say anything about the sling readings you got, but they are notorious for giving different readings for different individuals. #1 reason for erratic results was finding appropriate shade. Back in the day ERT training we broke several units with 25 firefighters slinging up next to pumper truck where the only shade was.  :lol: 


https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KAEX
https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=D5212&unit=0&timetype=LOCAL

So you're saying my Temp/Hum sensor is showing too wet?
Does local terrain/vegetation account for this? KAEX is 18 miles south of me and surrounded by miles of wide open dry cracked earth , and I'm in a deep hardwood forest near a swamp/lake.  Shouldn't I be reading a Higher dewpoint?
 And as far as shade to sling the psych. I got nothing but shade in my yard. You gotta search for sunny spot in the late afternoon  :grin:
« Last Edit: July 25, 2018, 09:13:09 PM by Bobvelle »

Offline ValentineWeather

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I can't say anything other than it does appear you are wetter.
Could be you have a good sensor and local geography makes it wetter.

I've just never seen it out of 8 different 31's they all act the same with exception some hit 100% others only 96%. 
I'm on my 3rd and final batch of baking 31's for reconditioning but out of the sensors I've tested the wet bias is still present.
 
I purchased all my sensors after the fact (not with station) could very well be there's a bad batch.

It's good you posted results, gives hope just maybe not all are bad and those complaining just have a bad batch.
Randy

Offline Bobvelle

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I can't say anything other than it does appear you are wetter.
Could be you have a good sensor and local geography makes it wetter.

I've just never seen it out of 8 different 31's they all act the same with exception some hit 100% others only 96%. 
I'm on my 3rd and final batch of baking 31's for reconditioning but out of the sensors I've tested the wet bias is still present.
 
I purchased all my sensors after the fact (not with station) could very well be there's a bad batch.

It's good you posted results, gives hope just maybe not all are bad and those complaining just have a bad batch.

Understood. The first 31 I had, about 2 years now, read 100% on only 2 or 3 occasions. The first time It happened, It was the first foggy night and I was watching it like a hawk. It took about 6 or 8 hours to go from 99% to 100% but it finally did hit it. This one is only a week old and conditions haven't been humid enough yet.

Edit to add: Now that I think about it, it was a passive shield setup at that time too. Nothing inferred with that just full disclosure. And also, on those 2 or 3 occasions it was early in its life. Haven't seen that in a while.
« Last Edit: July 25, 2018, 09:56:51 PM by Bobvelle »

Offline ValentineWeather

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Bobvelle where did you purchase the new 31?
Randy

Offline Bobvelle

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Bobvelle where did you purchase the new 31?

The latest and the older one both came from Ryan at Scaled Instruments.  The newest is the 25ft cabled version though. Which I doubt makes any difference.

Hey thanks for the MesoWest summery link. I never noticed it showed a wetbulb temp. Interesting.
« Last Edit: July 25, 2018, 10:19:32 PM by Bobvelle »

Offline ValentineWeather

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Bobvelle where did you purchase the new 31?

The latest and the older one both came from Ryan at Scaled Instruments.  The newest is the 25ft cabled version though. Which I doubt makes any difference.

Thanks
Randy

Offline jgentry

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I can't say anything other than it does appear you are wetter.
Could be you have a good sensor and local geography makes it wetter.

I've just never seen it out of 8 different 31's they all act the same with exception some hit 100% others only 96%. 
I'm on my 3rd and final batch of baking 31's for reconditioning but out of the sensors I've tested the wet bias is still present.
 
I purchased all my sensors after the fact (not with station) could very well be there's a bad batch.

It's good you posted results, gives hope just maybe not all are bad and those complaining just have a bad batch.

Understood. The first 31 I had, about 2 years now, read 100% on only 2 or 3 occasions. The first time It happened, It was the first foggy night and I was watching it like a hawk. It took about 6 or 8 hours to go from 99% to 100% but it finally did hit it. This one is only a week old and conditions haven't been humid enough yet.

Edit to add: Now that I think about it, it was a passive shield setup at that time too. Nothing inferred with that just full disclosure. And also, on those 2 or 3 occasions it was early in its life. Haven't seen that in a while.

A good SHT 31 (Davis version) does well when humidities hits in the 90s up to saturation. But thats about it. It will still have a wet bias at certain humidity and temperature  ranges. IMO.

As of now, Im planning on getting the SHT-75 for both of my stations and using it until Davis resolves the issues with their version of the SHT-31.

I think it would be a good idea for Davis to redo the transmitter, in so that, it can take pure I2C and use the SHT-35 (the one thats replacing the 75). Also use the SF2 filter cap. I think it would resolve their problems.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline ValentineWeather

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I have followed this forum for years, but never registered or even really considered posting. I have learned a great deal from following all of your comments and experiences over the years. So let me start by saying thank you. This particular topic, however, has brought me out of the shadows

I have owned Davis equipment since 2005. I bought a VP2. In 2006, I moved to south Texas and upgraded to a 24hr FARS and this is where my frustration with the dew point readings of the VP2 began. My new sensor would never hit 100% humidity and the rest of the scale had a wet bias, but my VP2 from 2005 never had these issues. My 2006 VP2 with FARS had an SHT11 and my 2005 had the old "analog" sensor.

I am no expert obviously, just another guy with a borderline unhealthy obsession with this stuff, but bottom line: my opinion and experience strongly supports that despite the inherent limitation of the Sensirion sensors, there is something about Davis' manufacturing process that causes an offset toward a wet bias.

I have been obsessed with trying to fix and find the source of this bias as well as trying to find a sensor that consistently hits 100% RH. The SHT11 had these issues and disappointingly so did the SHT31. I have moved around a bunch, so I have tested these things from anywhere from Texas to Maine to DC and to the Pacific Northwest. The result has always been the same. I have spent hours over the years with my sensors within 10 feet from the HO-1088 and DTS1 of an ASOS. I have purchased a psychro-dyne for quality checking. I have had the sensors in the -20sF in Maine and Vermont and over 100F in DC and Texas. Here are the main points of what I have learned:

-Outgassing of silicon and glue offsets the Sensirion sensor. The offset seems irreversible. Silicon offsets to the high side. Some glues to the low side. (I discovered this trying to use Sensirion's own filters instead of Davis' filter.)
-The Davis filter may increase response time, but is not responsible for the wet bias.
-The Sensirion sensors do seem to have a slight wet bias as has been documented in some studies, but this wet bias is some how exacerbated by how Davis mounts the sensor.
-The wet bias for Sensirion sensors in prolonged periods near saturation as mentioned in their datasheet is a separate issue from the wet bias created by the Davis mounting.
-The SHT75 straight from the manufacturer without any filter is superior to the Davis mounted SHT31 in terms of dew point and humidity.
-The SHT75 will hit up to 99%, with random very short lived jumps to 100%.
-I miss the old analog sensor

I currently run my station with an SHT75 with no filter at all. I've been doing it for about 6mos. The first 5 of those months were in a stock Davis 24hr FARS. Now it is in the Davis 7714, which is a surprisingly good passive shield (much better than the VP2 stock passive shield) (sometimes a degree or two cooler than the FARS, sometimes a degree or two warmer, at least in the north latitudes of the Seattle area...) I am concerned with contamination and dust, but after trying to put a filter on it with silicon and other glues, I have ruined a fair number of SHT75s with seemingly irreversible offsets. So far I have not seen any evidence of poor performance for lack of a filter.

I run a calibration in Cumulus for the SHT75 (1.041x-3) and field check it with the psychro-dyne. It generally is very close. The psychro-dyne is surprisingly accurate compared side by side to ASOS. I set Cumulus to report 98% as 100% and the calibration I set ensures 99% is reported as 100% too.

This is the best I have been able to do given the limitations of these sensors. I really hope the efforts here will force Davis to look at their process as I'd be happy to have an accurate Davis stock sensor that is engineered to last.

Hope this helps...

I can say I've always been told the Davis 7714 was a good passive shield and yes it blows the VP2 stock passive shield away. I just installed one today mid July at 43 near South Dakota border and running a full degree below both FARS shields and this is with very light winds.
This is over cut grass and 75-80F range currently with very high sun angle (straight up) July. Whether this changes once the sun is  low will wait and see this winter.

I'll never say a passive shield shouldn't be used again after testing this unit.  I did paint the inside bottom where sensor mounts and top inside flat black because I can never keep anything fully stock.  It's just an issue I have.    :oops:

Randy

Offline Old Tele man

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I have followed this forum for years, but never registered or even really considered posting. I have learned a great deal from following all of your comments and experiences over the years. So let me start by saying thank you. This particular topic, however, has brought me out of the shadows

I have owned Davis equipment since 2005. I bought a VP2. In 2006, I moved to south Texas and upgraded to a 24hr FARS and this is where my frustration with the dew point readings of the VP2 began. My new sensor would never hit 100% humidity and the rest of the scale had a wet bias, but my VP2 from 2005 never had these issues. My 2006 VP2 with FARS had an SHT11 and my 2005 had the old "analog" sensor.

I am no expert obviously, just another guy with a borderline unhealthy obsession with this stuff, but bottom line: my opinion and experience strongly supports that despite the inherent limitation of the Sensirion sensors, there is something about Davis' manufacturing process that causes an offset toward a wet bias.

I have been obsessed with trying to fix and find the source of this bias as well as trying to find a sensor that consistently hits 100% RH. The SHT11 had these issues and disappointingly so did the SHT31. I have moved around a bunch, so I have tested these things from anywhere from Texas to Maine to DC and to the Pacific Northwest. The result has always been the same. I have spent hours over the years with my sensors within 10 feet from the HO-1088 and DTS1 of an ASOS. I have purchased a psychro-dyne for quality checking. I have had the sensors in the -20sF in Maine and Vermont and over 100F in DC and Texas. Here are the main points of what I have learned:

-Outgassing of silicon and glue offsets the Sensirion sensor. The offset seems irreversible. Silicon offsets to the high side. Some glues to the low side. (I discovered this trying to use Sensirion's own filters instead of Davis' filter.)
-The Davis filter may increase response time, but is not responsible for the wet bias.
-The Sensirion sensors do seem to have a slight wet bias as has been documented in some studies, but this wet bias is some how exacerbated by how Davis mounts the sensor.
-The wet bias for Sensirion sensors in prolonged periods near saturation as mentioned in their datasheet is a separate issue from the wet bias created by the Davis mounting.
-The SHT75 straight from the manufacturer without any filter is superior to the Davis mounted SHT31 in terms of dew point and humidity.
-The SHT75 will hit up to 99%, with random very short lived jumps to 100%.
-I miss the old analog sensor

I currently run my station with an SHT75 with no filter at all. I've been doing it for about 6mos. The first 5 of those months were in a stock Davis 24hr FARS. Now it is in the Davis 7714, which is a surprisingly good passive shield (much better than the VP2 stock passive shield) (sometimes a degree or two cooler than the FARS, sometimes a degree or two warmer, at least in the north latitudes of the Seattle area...) I am concerned with contamination and dust, but after trying to put a filter on it with silicon and other glues, I have ruined a fair number of SHT75s with seemingly irreversible offsets. So far I have not seen any evidence of poor performance for lack of a filter.

I run a calibration in Cumulus for the SHT75 (1.041x-3) and field check it with the psychro-dyne. It generally is very close. The psychro-dyne is surprisingly accurate compared side by side to ASOS. I set Cumulus to report 98% as 100% and the calibration I set ensures 99% is reported as 100% too.

This is the best I have been able to do given the limitations of these sensors. I really hope the efforts here will force Davis to look at their process as I'd be happy to have an accurate Davis stock sensor that is engineered to last.

Hope this helps...

I can say I've always been told the Davis 7714 was a good passive shield and yes it blows the VP2 stock passive shield away. I just installed one today mid July at 43 near South Dakota border and running a full degree below both FARS shields and this is with very light winds.
This is over cut grass and 75-80F range currently with very high sun angle (straight up) July. Whether this changes once the sun is  low will wait and see this winter.

I'll never say a passive shield shouldn't be used again after testing this unit.  I did paint the inside bottom where sensor mounts and top inside flat black because I can never keep anything fully stock.  It's just an issue I have.    :oops:

All the solar radiation 'reflection' plates in our YPG tank-testing ambient air thermal-couple sensors had WHITE tops and flat-BLACK bottoms.
« Last Edit: July 26, 2018, 04:43:26 PM by Old Tele man »
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Offline ValentineWeather

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All the solar radiation 'reflection' plates in our YPG tank-testing ambient air thermal-couple sensors had WHITE tops and flat-BLACK bottoms.

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Randy

Offline openvista

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I can say I've always been told the Davis 7714 was a good passive shield and yes it blows the VP2 stock passive shield away. I just installed one today mid July at 43 near South Dakota border and running a full degree below both FARS shields and this is with very light winds.
This is over cut grass and 75-80F range currently with very high sun angle (straight up) July. Whether this changes once the sun is  low will wait and see this winter.

I'll never say a passive shield shouldn't be used again after testing this unit.  I did paint the inside bottom where sensor mounts and top inside flat black because I can never keep anything fully stock.  It's just an issue I have.    :oops:

Questions & observations.

First, you couldn't get a more basic "Gill" type shield. Ambient Weather has their own version (SRS100LX).

What did Davis do so wrong with their stock passive shield that it can't beat something that looks like it was designed and constructed in 8th grade science class?

Did you mount an SHTxx sensor in there? If so, how?

You recently modified the FARS shield to make it passive. You said it had amazing performance. How's it holding up?
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline Old Tele man

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I can say I've always been told the Davis 7714 was a good passive shield and yes it blows the VP2 stock passive shield away. I just installed one today mid July at 43 near South Dakota border and running a full degree below both FARS shields and this is with very light winds.
This is over cut grass and 75-80F range currently with very high sun angle (straight up) July. Whether this changes once the sun is  low will wait and see this winter.

I'll never say a passive shield shouldn't be used again after testing this unit.  I did paint the inside bottom where sensor mounts and top inside flat black because I can never keep anything fully stock.  It's just an issue I have.    :oops:

Questions & observations.

First, you couldn't get a more basic "Gill" type shield. Ambient Weather has their own version (SRS100LX).

What did Davis do so wrong with their stock passive shield that it can't beat something that looks like it was designed and constructed in 8th grade science class?

Did you mount an SHTxx sensor in there? If so, how?

You recently modified the FARS shield to make it passive. You said it had amazing performance. How's it holding up?
The SRS100LX has 9 plates spaced over 10.75-inches. That's a little over 1-inch spacing between each plate and the plate "lips" are deeper than each plate-to-plate spacing, so there's LOTS of air flow capability. Years ago I used one with my LaCrosse WS-8610U system once I figured out that their crappy unit was totally worthless.
« Last Edit: July 26, 2018, 06:41:33 PM by Old Tele man »
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Offline openvista

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The SRS100LX has 9 plates spaced over 10.75-inches. That's a little over 1-inch spacing between each plate and the plate "lips" are deeper than each plate-to-plate spacing, so there's LOTS of air flow capability. Years ago I used one with my LaCrosse WS-8610U system once I figured out that their crappy unit was totally worthless.

The problem out this way with more spacing is it makes it easier for wind-driven snow to get in and sit on the sensor.
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline Old Tele man

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The SRS100LX has 9 plates spaced over 10.75-inches. That's a little over 1-inch spacing between each plate and the plate "lips" are deeper than each plate-to-plate spacing, so there's LOTS of air flow capability. Years ago I used one with my LaCrosse WS-8610U system once I figured out that their crappy unit was totally worthless.

The problem out this way with more spacing is it makes it easier for wind-driven snow to get in and sit on the sensor.

Seldom snows here in High Deserts of AZ -- but it does snow on rare occasions -- it's summer heat, not winter snow, that's our problem.
« Last Edit: July 26, 2018, 05:45:36 PM by Old Tele man »
SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB;
DBX2 & DBX1 Precision Digital Barographs
CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
WU - KAZTUCSO202, Countryside

Offline ValentineWeather

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I can say I've always been told the Davis 7714 was a good passive shield and yes it blows the VP2 stock passive shield away. I just installed one today mid July at 43 near South Dakota border and running a full degree below both FARS shields and this is with very light winds.
This is over cut grass and 75-80F range currently with very high sun angle (straight up) July. Whether this changes once the sun is  low will wait and see this winter.

I'll never say a passive shield shouldn't be used again after testing this unit.  I did paint the inside bottom where sensor mounts and top inside flat black because I can never keep anything fully stock.  It's just an issue I have.    :oops:

Questions & observations.

First, you couldn't get a more basic "Gill" type shield. Ambient Weather has their own version (SRS100LX).

What did Davis do so wrong with their stock passive shield that it can't beat something that looks like it was designed and constructed in 8th grade science class? I tested the VP2 stock couple years ago and was running very warm +3 at times.

Did you mount an SHTxx sensor in there? If so, how? Yes, same place designed for a metal probe in middle but just used 1 screw and not bracket for metal probe

You recently modified the FARS shield to make it passive. You said it had amazing performance. How's it holding up? It did really well until it got calm and then was running +2. Still better than the stock VP2 I would say.

I feel passive shields may give mixed results depending on longitude, siting placement over bare ground, sand, grass & wind speed. I may hate the shield at 100 but today it's still better than the fars barely, currently no wind


« Last Edit: July 26, 2018, 05:54:50 PM by ValentineWeather »
Randy

Offline openvista

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Thanks for the info!

What did Davis do so wrong with their stock passive shield that it can't beat something that looks like it was designed and constructed in 8th grade science class? I tested the VP2 stock couple years ago and was running very warm +3 at times.

I was just looking at the VP2 specs where Davis admits that at 1040 w/m2 insolation the stock shield can reach +4F errors. I've seen worse over fresh snow (6F+ compared to my FARS).
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline CW2274

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Thanks for the info!

What did Davis do so wrong with their stock passive shield that it can't beat something that looks like it was designed and constructed in 8th grade science class? I tested the VP2 stock couple years ago and was running very warm +3 at times.
I've seen worse over fresh snow (6F+ compared to my FARS).
Many folks are under the impression that a FARS only benefits hot climates. I got to the point where I quit trying. ](*,)

 

anything